The present invention relates to apparatus for a vehicle seat backrest.
Conventional backrests for vehicle seats are provided with resilient compliant means having only a comfort function, i.e. they are functional to provide an even and comfortable support for the passenger""s back and will adapt to normal back motions during a normal state of use. In case of a rear-end collision, the back will be subjected to excessive rearwards movement in the backrest, and, furthermore, accumulation of resilient energy will cause the back to recoil forward, creating a risk of so called whiplash injuries.
From International Application No. WO 95/11818 a backrest is known, which has been designed with the aim of reducing whiplash injuries caused by rear-end collisions. According to the prior art, this has been achieved by arranging separate stroke-limiting means, such as bands or links having attachment points separate from the fastening points of the springs. The means of attachment and the design of the spring means and the stroke-limiting means are very critical with regard to the total function of compliance of the backrest, for normal loads as well as extreme loads, such as during a collision.
An object of the present invention is to provide apparatus for a backrest in which the compliant members can have accurately specified properties.
In accordance with the present invention, this and other objects have now been realized by designing the compliant member of such backrests with each spring member and stroke limiting member being integral components which can be produced with specified properties with respect to their compliance characteristics.
In accordance with the present invention, applicants have invented a backrest for a vehicle seat comprising a frame defining a central zone, a support member, a plurality of compliant members for supporting the support member within the central zone, whereby the compliant members and the support member can absorb the load from a person seated in the vehicle seat, the plurality of compliant members comprising a resilient spring member and a corresponding stroke-limiting member for permitting the resilient spring member to move through a predetermined stroke and absorb a load within a first load range and limiting further stroke of the resilient spring member within a second load range, one of the resilient spring member and the stroke-limiting member including a first fastener for attachment to the frame and one of the resilient spring member and the stroke-limiting member including a second fastener for attachment to the support member. In a preferred embodiment, at least one of the plurality of compliant members comprises a plastically compliant member whereby the one of the plurality of compliant members exhibits plastic compliance at a load exceeding the second load range. Preferably, the plastically compliant member is disposed in series with one of the resilient spring members. In another embodiment, however, the plastically compliant member is disposed in parallel with one of the resilient spring members. Preferably, one of the stroke-limiting members is disposed in series with the plastically compliant member.
In accordance with one embodiment of the backrest of the present invention, the backrest includes stroke-limiting means for limiting further stroke of the resilient spring member within a third load range above the load exceeding the second load range.
In accordance with another embodiment of the backrest of the present invention, the resilient spring member comprises a coil-type compression spring and wherein the stroke-limiting member comprises first and second fastening members, the first fastening member including a first end including the first fastener and the second fastening member including a first end including the second fastener. In a preferred embodiment, the first and second fastening members extend through the coil-type compression spring, the first fastening member including a second end attached to one end of the coil-type compression spring and the second fastening member including a second end attached to the other end of the coil-type compression spring, whereby motion of the first and second fastening members causes compression of the coil-type compression spring such that stroke-limiting occurs upon complete compression of the coil-type compression spring.